Root-knot nematode infests up to 65 percent of California's vineyard acreage, weakening vines, reducing vine establishment and ultimately limiting productivity. Even nematode resistant rootstocks, such as Harmony and Freedom, have become susceptible to this aggressive type of nematode.

Researchers at Cornell University's Grape Genetics Research Unit in Geneva, N.Y., are looking at wild grape materials from the tropics and subtropics to develop resistant new rootstocks that will protect against root-knot nematode. Resistant traits from these wild materials can be crossed over many generations with domestic Vinifera species to isolate for resistance while breeding out rank growth and other negative cultural characteristics.

Root-knot nematodes damage vines by burrowing into grapevine roots. The roots swell and crack, reducing their ability to take up water and nutrients and providing a pathway for secondary pathogens.

These aggressive nematodes can lay up to 2,000 eggs, which hatch and move through the soil looking for new uninfested roots. Pre-plant fumigation and soil drenches can help limit the spread of root-knot nematode, but the long-term solution lies in resistant rootstocks. Resistant rootstocks are not only more environmentally friendly, but will provide systemic protection throughout the life of the vineyard.

Grape rootstocks have long provided protection against soil borne pests and diseases. The grape industry first used rootstocks to turn the tide on phylloxera, an insect that also feeds on the roots of vines. It's an arduous, time-consuming process, but geneticist Peter Cousins, a grape rootstock researcher with the USDA's Agricultural Research Service, told growers at the recent San Joaquin Valley Grape Symposium that researchers are well on their way to isolating traits from resistant rootstocks that can be incorporated into new rootstocks for grape producers in California.

“In our breeding program we are looking to combine nematode resistance with good horticultural characteristics like easy rooting, grafting and phylloxera protection that are found in our commercial rootstocks,” Cousins said. “We are selecting for resistant rootstocks that have resistance superior to Freedom and are able to perform well in the vineyard.”

At the Cornell research center, Cousins and his team have made hundreds of crosses with wild and commercial rootstocks and selected the most promising cultivars for further study. About 5 percent of those crosses move on to the field research level and Cousins now has trials at the UC Kearney Ag Center in Parlier to determine the vineyard performance of the most promising selections. Once these experimental rootstocks have been through field trials, they are sent to the virus testing program at Foundation Plant Services, UC Davis, to determine if they are free of viruses.

“These are now in replicated trials in the San Joaquin Valley and we have entered into the advanced stages of testing to see if they will be adequate to provide root-knot nematode resistant rootstocks,” he said. “These rootstocks have nematode resistance coming from different sources and we are interested in looking at resistance, but also propagation ability and cultural performance of grafted grapevines in the vineyard.”

Cousins is currently seeking grower cooperators throughout California to participate in on-farm rootstock trials in commercial vineyards.

In addition to isolating for root-knot nematode resistance, Cousins said USDA's Grape Genetics Research Unit is also focused on finding vigorous rootstocks that can withstand drought type conditions in the vineyard.

“Right now we have fairly good sources of water and our water quality is quite good compared to other parts of the world, but it seems likely that that is going to change,” he said. “More vigorous rootstocks in the future could be a useful way to compensate for less water or lower water quality in San Joaquin Valley viticulture.”

The University of California Cooperative Extension put on the symposium. It was sponsored by the California Raisin Marketing Board.